1. Field of the Invention
The present invention relates to a method for manufacturing a silicon-on-insulator (SOI) substrate, an SOI substrate, and a method for manufacturing a semiconductor device including the SOI substrate.
2. Description of the Related Art
In recent years, instead of a bulk silicon wafer, the use of a silicon-on-insulator (SOI) substrate where a thin single crystal semiconductor layer is provided over an insulating surface has been considered. Because parasitic capacitance generated by a drain of a transistor and a substrate can be reduced by use of an SOI substrate, SOI substrates have attracted great attention as substrates which improve performance of semiconductor integrated circuits.
One of known methods for manufacturing SOI substrates is a Smart Cut (registered trademark) method (for example, see Patent Document 1). A summary of a method for manufacturing an SOI substrate by a Smart Cut method is described below. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method; thus, a microbubble layer is formed at a predetermined depth from the surface. Next, the silicon wafer into which hydrogen ions are implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. After that, through heat treatment, part of the silicon wafer into which hydrogen ions are implanted is separated in a thin film shape along the microbubble layer. Accordingly, a single crystal silicon film is formed over the other bonded silicon wafer.
Further, a method for forming a single crystal silicon layer over a base substrate made of glass by using such a Smart Cut method has been proposed (for example, see Patent Document 2). Glass substrates may have larger sizes and are less expensive than silicon wafers; thus, glass substrates are mainly used in manufacturing liquid crystal display devices and the like. By using a glass substrate as a base substrate, a large-sized inexpensive SOI substrate can be manufactured.